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Weekly vegetable update – July 10, 2024

Authors: Marissa Schuh and Natalie Hoidal

The season hums along with growers harvesting, planting, and managing a variety of pests. Read on for information about deciding what to replant as fields dry out, aster yellows, and the trinity of vine crop insect pests.

General Notes
Most of Minnesota is on deck for the hottest sustained temperatures we’ve seen this summer. Make sure you’re taking care of yourself, your employees, volunteers, or anyone else on the farm by paying attention to the wet bulb temperature, which factors in temperature, humidity, wind speed, sun angle and cloud cover. Download the OSHA-NIOSH heat safety tool to get your location's heat index and risk at any given time. If you don't have a smartphone, consider purchasing a wet bulb thermometer for your farm. Wet bulb thermometers provide a more accurate measure of the “real feel” than temperature alone. Based on this temperature, follow the chart below to make sure you’re taking enough breaks and drinking enough water to prevent heat stress. These guidelines are from OSHA, and are based on a healthy individual under age 40 wearing normal work clothing. If you have any sort of health condition that makes you more sensitive to heat, have to wear protective clothing, or are working in an especially hot area, take extra precautions. Find the table and more info at:

Many growers are thinking about replanting as their fields finally dry out.  When figuring out what to plant and what varieties to use, remember that fall is not as far away as it may seem (gulp). Make sure to cross check days to maturity of what you are planting against the date of the  the first frost. This is especially important for frost sensitive crops. You can check the frost probabilities for your area with the DNR's Final Spring / First Fall Freeze Data Probabilities tool. For example, for where I work in Farmington, there is a 10% chance the first frost (32F) by 9/27, 50% chance by 10/10, and a 90% chance frost will have happened by 10/25.  Conservatively there are 79 days left of the growing season between today and the 10% chance of frost date.  This means I want varieties that have estimated days to maturity of 79 or less, at least for stuff that isn't cold hardy. 

Crop Updates
Carrots for fall harvest are being planted. Fall carrot timing is always a gamble, since they become sweeter after a frost, but if we happen to get a lot of rain in the fall, it can be hard to get into the field for harvest later in the season. The best bet for many growers is to simply plant at least a few successions. Make a note that aster yellows is around this year, see the linked article for tips on monitoring and management.

Garlic harvest is on the horizon for many farms. Wondering if you're ready to harvest? There are two main ways to determine whether your garlic is ready: when about half of the leaves turn brown is a fairly reliable indicator of maturity. You can also harvest a few bulbs and cut them in half. If the cloves fill the skin, they are ready.
Garlic with discolored wrapped due to aster yellows. Photo: UMN Extension. 

Garlic on some farms is looking off – it could be aster yellows, it could be nutritional issue, it could be a couple of other things. If you plan on saving garlic to plant yourself or selling it for others to plant, send a sample to the diagnostic lab to make sure you don’t have a pathogen that can survive in the cloves.

Pepper plants on a couple of farms are looking unhappy – spindly, not very bushy despite setting fruit, and not the deep green we hope to see. This may be nutritional – we’ve written a lot this year about the rain causing nutrient leaching – but it could also just be the weather in general. Peppers like it hot, and most of Minnesota hasn’t seen that many days over 85. Peppers also hate having “wet feet,” and the sustained soil moisture from the regular rains makes peppers unhappy. If you’re trying to figure out if it is a nutrient deficiency or something else, look at whatever is next door to your peppers. Are those plants looking healthy and happy, or are they looking lightly colored and stressed as well? If they look happy, it is probably just peppers acting as peppers are going to act when the weather is like this.  If everything looks a little off, consider an application of N.

For potatoes and tomatoes, late blight has been found in Ontario.  This disease is very destructive, but doesn't make it very far north many years.  We still have a ways to go this growing season, so keep an eyes out for late blight symptoms when scouting. We will post updates here if this disease makes its way westward.

Sweet corn harvest has started on some farms. If you have sweet corn that will be picked soon, remember that before corn is ready is the time to do animal deterrents. If you have a history of problems with wildlife, install your scare tactics before the animals get a chance to discover how good your corn is. Once they get a taste, it is incredibly hard to keep them out.

Farming near a marsh? Red winged blackbirds are likely to cause damage in neighboring sweet corn. Photo: Joy Viola, Northeastern University,

Vine crops are entering the period where all three of the major insect pests are active. 

Cucumber beetles are still damaging leaves and in some cases fruit, but many are turning their interest to flowers, which doesn't damage yields.

I saw my first squash vine borer of the season in the Twin Cities metro in the last week. She was laying eggs on zucchini– the eggs were numerous, circular, and flattened. For small plantings you sometimes see recommendations to remove eggs, which may be impractical as the eggs look like a grain of sand. Other management options are equally impractical – some growers in very small plantings physically extract larvae, which can open up the plant to other problems.

Adults squash vine borers fly during the day and looks like wasps, IF you have things buzzing around your field that doesn't seem to be too interested in flowers, take a moment to watch them -- they may be a squash vine borer. Pictured here, one lays an egg. Photo: Brantlee Spakes Richter, University of Florida,

This is a hard pest to manage with insecticides – the only time when they are able to be touched by insecticides is between eggs hatch and burrowing in the crown – a very small, hard to predict window.  The insects also lays eggs over a the period of a few weeks, so this window can happen multiple times.

Come on and feel the eye strain. A squash vine borer eggs on zucchini (circled). Photo: Marissa Schuh, UMN Extension,

For growers in smaller areas, this insect can be a persistent problem. Varieties that vine out quickly and set roots at the nodes of the vines can sometimes get enough from those roots to survive and still be productive even if the main plant stem has been bore into. Succession planting and planting more plants than you need, anticipating the loss of some of them, can also help.

Squash bugs and their eggs are also being found. Eggs are coppery and laid in groups, scrape them as you see them. If you are seeing an average of one egg mass per plant, consider making an application next week as eggs start to hatch. The nymphs are the easiest to kill with insecticides, and if you knock back the populations early, you will see less of the leaf damage they do later in the season when the insects are larger/more hungry/more capable of hurting plants/harder to manage with insecticides.
Squash bugs nymphs hatching from eggs. Photo: Bruce Watt, University of Maine,

Finally, this is the time of year when we can start to see powdery mildew. If you have had major losses in the past, catching this disease early is key in effective fungicide use. Look on the underside of the oldest leaves in the densest part of the canopy, start scouting as your crops set fruit.

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